The present invention relates to a sensor for automatic doors. Particularly, the present invention concerns measures to simplify sensor installation.
With respect to an automatic door which opens and closes along a track, an object detection range is usually set on the interior and the exterior of the doorway, and objects in the detection range are detected by an activation sensor. As the activation sensor, there are generally known varieties like sensor mats, ultrasonic sensors and pyroelectric sensors. The activation sensor is turned on when it detects entry of an object within the detection range, and operates to open the door.
Additionally, an auxiliary safety sensor which utilizes a beam (e.g. infrared ray) is installed in the vicinity of the track of the door, between the interior and exterior detection ranges. An example of the auxiliary safety sensor is disclosed in Japanese Patent Laid-open Publication No. 2000-320243. This auxiliary safety sensor is mounted on a pair of posts which stand on both sides of the doorway, in such a manner that a transmitter on one of the posts is positioned face to face with a receiver on the other post. In this structure, when a light beam is emitted from the transmitter towards the receiver and interrupted by something, the receiver fails to receive the light beam. The sensor regards this condition as the presence of an object near the door track. Based on this recognition, the auxiliary safety sensor holds the door open even if the activation sensor is turned off. The auxiliary safety sensor is effective, for example, when a person stops on the door track. In this situation, the activation sensor is turned off, because this person's body is out of the interior and exterior detection ranges. Nevertheless, the auxiliary safety sensor can detect the person and keep the door open, thereby avoiding unexpected closure of the door.
As for installation of this type of auxiliary safety sensor, the transmitter and the receiver are equipped on the respective posts and have their signal lines passed inside the posts. Terminals at the ends of these signal lines are connected to a terminal block in an automatic door controller which is accommodated in a transom.
In order to enhance the reliability of object detection, this type of the auxiliary safety sensor may utilize two sensor sets, each of which is composed of a transmitter and a receiver. In a typical embodiment, the first sensor set (the first transmitter and the first receiver) and the second sensor set (the second transmitter and the second receiver) are provided at different heights. For this auxiliary safety sensor equipped with two sensor sets, the transmitters have their light emission timings (timings of generating light emission pulses) delayed from one another, in an attempt to ensure reliable light emission/acceptance actions at each sensor set (i.e. intended to prevent either receiver from operating in response to the light emitted from the other sensor set). In other words, the auxiliary sensor determines the absence of an object only when each receiver receives light in synchronization with the light emission timing of the opposite transmitter.
Regarding the installation of the auxiliary safety sensor with two sensor sets, two transmitters are equipped on one post and two receivers are mounted on the other post. Signal lines extending from these transmitters and receivers are passed inside the posts, so that each post contains two signal lines. Terminals (four terminals in total) at the ends of the signal lines are connected to a terminal block in an automatic door controller which is housed in a transom.
However, it is confusing to establish connection between the terminal block and the two signal lines passed inside each post. Namely, a worker may not be sure of the correlations between the transmitters and the signal lines in the first post (i.e. to find out which signal line comes from which transmitter), and the correlations between the receivers and the signal lines in the second post (i.e. to find out which signal line comes from which receiver). Thus, the sensor installation operation may end in misconnection, in which state the terminals are not connected to predetermined connection points at the terminal block in the automatic door controller. An example of misconnection is shown by the broken lines in FIG. 3 (the view showing how the transmitters 61, 62 and the receivers 63, 64 are connected to the terminal block 7). In this example, the signal line 63a coming from the first receiver 63 is connected to the connection point 74 for the second receiver 64, while the signal line 64a extending from the second receiver 64 is connected to the connection point 73 for the first receiver 63. In terms of signal processing, the first transmitter 61 and the second receiver 64 constitute a sensor set, and the second transmitter 62 and the first receiver 63 are paired as another sensor set, in a wrong manner. The transmitters and the receivers in these sensor sets are not opposed to each other. As a result, when the first receiver 63 receives a light beam produced at a given emission timing by the first transmitter 61, light acceptance data acquired by the first receiver 63 are inputted into the connection point 74 for the second receiver 64. Because this input does not coincide with a given acceptance timing, the sensor judges that no light is received. Similarly, when the second receiver 64 receives a light beam produced at a given emission timing by the second transmitter 62, light acceptance data acquired by the second receiver 64 are inputted into the connection point 73 for the first receiver 63. Because this input does not coincide with a given acceptance timing, the sensor judges that no light is received. While both sensor sets determine that the emitted light beams are interrupted by an object, the auxiliary safety sensor prohibits the closing action of the door, constantly leaving the door open. Unfortunately, it is impossible to notice the misconnection before an actual test operation of the automatic door. If misconnection is found by the operation test, a worker has to reconnect the signal lines, which complicates the sensor installation.
Various ideas have been suggested to prevent the misconnection. For one, signal lines of different colors can be employed. For another, tags can be attached to the signal lines in order to distinguish the sensor sets. In the former method, however, a worker has to bear a heavier burden of remembering the colors of the signal lines when he or she mounts the transmitters and the receivers on the posts. Besides, the latter method is detrimental to the operability, because the tags hinder the passage of the signal lines through the posts.